Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$108.39	3.258%	$111.9213	$111.92	$111.90	$111.90
Purchase #2	$175.65	5.826%	$185.8834	$185.88	$185.90	$185.90
Purchase #3	$26.83	5.321%	$28.2576	$28.26	$28.25	$28.30
Purchase #4	$86.71	10.266%	$95.6116	$95.61	$95.60	$95.60
Purchase #5	$66.45	6.449%	$70.7354	$70.74	$70.75	$70.70
Purchase #6	$84.84	12.479%	$95.4272	$95.43	$95.45	$95.40
Purchase #7	$212.84	10.791%	$235.8076	$235.81	$235.80	$235.80
7 purchase totals =	$761.71		$823.6441	$823.65	$823.65	$823.60